1. Field of the Invention
The present invention generally relates to an ink-jet head, and, in particular, to an electrostatic ink-jet head.
2. Description of the Related Art
An ink-jet head used in an ink-jet recording apparatus used as an image recording apparatus (image forming apparatus) such as a printer, a facsimile machine, a copier, a plotter or the like includes nozzle holes through which ink drops are fired, firing chambers (also called pressure chambers, pressurizing liquid chambers, liquid chambers, ink flow paths or the like) with which the nozzle holes communicate, and energy generating mechanisms which generate energy for pressurizing the ink in the discharge chambers. As a result of the energy generating mechanisms being driven, the ink in the discharge chambers is pressurized, and ink drops are fired therefrom through the nozzle holes. An ink-on-demand system in which ink drops are fired only at a time of recording is mainly employed.
In the related art, as the energy generating mechanisms which generate energy for pressurizing the ink in the firing chambers, one in which vibration plates as walls of the firing chambers are deformed through piezoelectric devices, and the volumes of the firing chambers are changed, and ink drops are fired therefrom (see Japanese Patent Publication No. 2-51734), or one in which ink is heated in the firing chambers through heating resistance elements, bubbles are generated, thereby the pressures in the chambers are increased, and ink drops are fired therefrom (see Japanese Patent Publication No. 61-59911) are known.
In the former system in which the piezoelectric devices are used, a process of sticking chips of the piezoelectric devices to the vibration plates for generating pressures in the firing chambers is complicated, and, also, it is not possible to greatly improve printing speed and printing quality. In the latter system in which ink is heated, although the problems involved in the system using the piezoelectric devices do not occur, the heating resistance elements are damaged due to repetition of rapid heating and cooling, and a shock at a time when bubbles burst. Thereby, the life of the ink-jet head is short in general.
In order to solve these problems, as disclosed in Japanese Laid-Open Patent Application No. 6-71882 and so forth, an ink-jet head is proposed in which vibration plates as walls of the firing chambers and electrodes are arranged in parallel (gaps formed therebetween being referred to as xe2x80x98parallel gapsxe2x80x99), the vibration plates are deformed by electrostatic forces generated between the vibration plates and electrodes, thereby the volumes of the firing chambers are changed, and ink drops are fired therefrom.
Such an electrostatic ink-jet head in the related art has, as shown in FIGS. 1 and 2, a substrate 101 which includes pressurizing chambers 102, vibration plates 103 as walls of the pressurizing chamber 102, a common ink chamber 104 which supplies ink to the pressurizing chambers 102, an ink supply path 105 through which the common ink chamber 104 and pressurizing chambers 102 communicate, and so forth. Further, in this ink-jet head, silicon oxide films 112 are formed on an electrode substrate 111 of a borosilicate-glass substrate or a silicon substrate, electrodes 113 facing the vibration plates 103 are formed on the silicon oxide films 112, and the surfaces of the electrodes 112 are covered by insulating films 114. Then, the substrate 101 and electrode substrate 111 are bonded together with the silicon oxide films 112 provided therebetween. Further, a nozzle plate 121 is bonded onto the substrate 101, and has nozzle holes 122 which communicate with the pressurizing chambers 102 and an ink supply hole 123 which supplies ink to the common ink chamber 104 formed therein.
Further, in order to use the vibration plates 103 as a common electrode, as shown in FIG. 1, an electrode-connecting area 106 for the common electrode is provided in the substrate 101 at an end thereof in a nozzle-arranged direction, and, in order to use the electrodes 113 as individual electrodes, the electrodes 113 are extended to the end of the electrode substrate 111, and electrode pads 116 are formed. A portion of the substrate 101 is removed above the electrode pads 116.
In the above-described electrostatic ink-jet head in the related art, it is necessary to provide the electrode-connecting area so as to use the vibration plates as the common electrode. Thereby, the area of the head increases. Further, because the gaps between the vibration plates and electrodes are formed using the silicon oxide films as gap spacers as they are, it is difficult to control the gaps through a wide range, and to make design suitable for desired operation (vibration) characteristics of the head.
The present invention has been devised in consideration of the above-mentioned matters, and, an object of the present invention is to miniaturize an ink-jet head and to reduce a variation in vibration characteristics of the ink-jet head.
In order to solve the above-mentioned problems, in an ink-jet head according to the present invention, electrodes facing vibration plates are provided on an electrode substrate having conductivity with an insulating layer provided therebetween, and the electrode substrate and vibration plates are electrically connected together.
Thereby, it is possible to use the electrode substrate as a common electrode, to miniaturize the head, and to reduce variation in ink-drop-firing characteristics among bits.
Here, the electrical connection of the electrode substrate and vibration plates may be made as a result of the electrode substrate being bonded to the vibration plates without an insulating layer provided therebetween. Thereby, it is possible to electrically connect the electrode substrate and vibration plates together stably with high reliability. In this case, the electrode substrate and vibration plates may be formed from silicon substrates, and both the silicon substrates may be bonded together directly. Thereby, a warp and/or coming off due to a difference in thermal expansion coefficient does not take place therein, and the gap accuracy can be secured. Alternatively, the electrode substrate and vibration plates may be formed from silicon substrates, and both the silicon substrates may be bounded together by eutectic bonding through a metal. Thereby, the gap accuracy can be secured, and, also, the resistance of the vibration plates is reduced.
In this case, it is preferable to use a single-crystal silicon substrate having a crystal plane orientation (100) as the electrode substrate. Thereby, it is possible to improve design flexibility in gap formation using anisotropic etching, and, also, to easily form variable gaps (gaps having variable gap lengths).
Further, it is also preferable to use a single-crystal silicon substrate having a crystal plane orientation (110) as the electrode substrate. Thereby, it is possible to improve design flexibility in gap formation using anisotropic etching, and, also, to obtain stable vibration characteristics.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.